In one known type of I/P converter (hereinafter referred to as "an electromagnetic I/P converter of the type described"), the fluid pressure output is varied in dependence upon an electrical input signal applied to an annular electromagnetic coil which is operatively associated with a "flapper" that co-operates with a fluid exhaust nozzle. The coil co-operates with a permanent magnet assembly and assumes an axial position relative to the magnet assembly in dependence upon the magnitude of the electrical input signal. Thus, the flapper assumes a corresponding position nearer to or further from the exhaust nozzle, as the case may be, and creates a variable back pressure within the nozzle which, in turn, is dependant upon the magnitude of the electrical input signal. This back pressure determines, via a piston or diaphragm assembly, the degree of opening of the converter's main valve assembly and therefore the fluid output pressure of the converter.
In one commonly used construction of I/P converter of the type described, the electromagnetic coil is secured to the upper surface of one end of a lever pivotally mounted on a fulcrum and the other end of the lever carries the flapper on its lower surface, the flapper co-operating with the exhaust nozzle which is located below it. Such a construction is not particularly compact and suffers from the serious problem that, because it utilises a fulcrum/lever arrangement, it is very sensitive to external vibrations. This problem can be solved by providing a closed-loop control arrangement but the converter is then significantly more expensive to produce.
In an improved construction devised by us and which is embodied in our prior 100 Series I/P converters, the fulcrum/lever arrangement is replaced by an annular flexure fixedly secured at its periphery and having an integral flexible central portion that carries a separately formed flapper, the coil being mounted on the upper surface of the flexible central portion and the flapper co-operating with the fluid exhaust nozzle which is located below the central portion of the flexure. Whilst such a construction is less susceptible to external vibrations, it is not particularly compact.
It is an object of the present invention to provide an improved, relatively compact, cost-effective design of electromagnetic I/P converter of the type described that, especially, does not suffer to any significant extent from the problem associated with external vibrations whether or not it incorporates closed-loop control. As will become apparent, preferred features of the design afford other significant advantages over prior designs.